Not only are many anatomical and physiologic measures being now demonstrated to show fractal characteristics, but the behavior of biological systems is being recognized not to be nicely periodic, and more likely to be unpredictable with any precision. This wandering or variability is not due to irregular inputs from external to the system but is inherent in the system itself, independent of noise, and is attributable to the nonlinearities and delays in the interactions between components of the system. It is the purpose of this project to take some of the methods being used for assessing chaotic system behavior, particularly those which do not show period doubling or bifurcations, and to develop their applications to physiologic systems related to cardiovascular mass transport, exchange and metabolism.